F12 Control of Gene Expression.pptx - Harrison High School

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Dec 14, 2012 (4 years and 6 months ago)

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Control of Gene Expression

Cloning

S0matic cell nuclear transfer


Researchers clone animals by
nuclear
transplantation


SOMATIC CELL NUCLEAR TRANSFER:

A nucleus of an egg cell is
replaced with the nucleus of a somatic cell from an adult


Thus far, attempts at human cloning have not
succeeded in producing an embryo of more than six
cells


Embryonic development depends on the
control of gene
expression

(aka protein synthesis)

Somatic Cell Nuclear Transfer


In
reproductive cloning
, the embryo is implanted in a
surrogate mother. The goal is to
produce a cloned
offspring.


In
therapeutic cloning
, the idea is to
produce a source
of embryonic stem cells.


Stem cells can help patients with damaged tissues.


Stem cells are NOT specialized in structure and function
,
therefore they can take on the role of damaged cells in
damaged tissues.

Reproductive vs. Therapeutic Cloning

Remove

nucleus

from egg

cell

Donor

cell

Add somatic

cell from

adult donor

Grow in culture to produce

an early embryo (blastocyst)

Nucleus from

donor cell

Implant blastocyst

in surrogate mother

Remove embryonic

stem cells from

blastocyst and

grow in culture

Clone of donor

is born

(REPRODUCTIVE

cloning
)

Induce stem

cells to form

specialized cells

for
THERAPEUTIC

use

Dolly the Sheep

Reproductive vs. Therapeutic Cloning

Genetic Regulation in
Prokaryotes


Proteins interacting with DNA turn prokaryotic genes
on
or off
in response to environmental
changes.


The process by which genetic information flows from
genes to proteins is called
gene
expression
.


Our earliest understanding of gene control came from the
bacterium
E.
coli


(Reminder: Bacteria are prokaryotes.)

Proteins turn genes on or off

Cellular Differentiation & the
Cloning of Eukaryotes


Differentiation

yields a variety of cell types, each
expressing a different combination of
genes


In multicellular eukaryotes, cells become specialized
as a zygote develops into a mature organism


Different types of cells make different kinds of
proteins.


Different combinations of genes are active in each
type.

Cellular Differentiation


Differentiated cells may retain all of their
genetic
potential
.
(Even if turned off, the gene is still present.)


Most
differentiated cells retain a complete set of genes


In general, all
somatic cells
of a multicellular organism have
the same
genes.


So a carrot plant can be grown from a single carrot cell.

Retain Genetic Potential


The cloning of tadpoles showed that the nuclei of
differentiated animal cells retain their full genetic
potential


Early Nuclear Transfer

Tadpole (frog larva)

Intestinal cell

Frog egg cell

Nucleus

Nucleus

UV

Nucleus

destroyed

Transplantation

of nucleus

Eight
-
cell

embryo

Tadpole


The first mammalian clone, a sheep named
Dolly
, was
produced in 1997


Dolly provided further evidence for the developmental
potential of cell nuclei.

Dolly again


Connection: Reproductive cloning of nonhuman
mammals has applications in
basic research,
agriculture, and
medicine
.


Scientists
clone farm animals with specific sets of
desirable
traits.


Piglet clones might someday provide a source of organs
for human
transplant.

Applications of Nonhuman
Mammalian Cloning


Connection: Because stem cells can both perpetuate
themselves and give rise to differentiated cells, they
have great
therapeutic
potential


Adult stem cells can also perpetuate themselves in
culture and give rise to differentiated cells


But they are harder to culture than embryonic stem
cells.


They generally give rise to only a limited range of cell
types, in contrast with embryonic
stem cells.

Therapeutic Cloning


Differentiation of embryonic stem cells in culture

Cultured

embryonic

stem cells

Different culture

conditions

Different types of

differentiated cells

Heart muscle cells

Nerve cells

Liver cells


DNA packing in eukaryotic chromosomes helps
regulate gene
expression.


A chromosome contains a DNA double helix wound
around clusters of
histone
proteins.


DNA packing tends to block gene
expression.


Gene Regulation in Eukaryotes

DNA

double

helix

(2
-
nm

diameter)

Metaphase chromosome

700

nm

Tight helical fiber

(30
-
nm diameter)

Nucleosome

(10
-
nm diameter)

Histones

“Beads on

a string”

Supercoil

(200
-
nm diameter)


In female mammals, one X chromosome is inactive in each
cell.


An extreme example of DNA packing in interphase cells is
X
chromosome inactivation


Female Mammals

EARLY EMBRYO

Cell division

and

X chromosome

inactivation

X chromosomes

Allele for

orange fur

Allele for

black fur

TWO CELL POPULATIONS

IN ADULT

Active X

Inactive X

Orange fur

Inactive X

Active X

Black fur

Genetic Biotechnology


Since ancient times, humans have bred animals and plants to increase
the likelihood of certain desirable traits.


Example: Hunting dogs or larger fruits


Two methods are used:


Hybridization
: crossing different parent organisms with different forms
of a trait to produce an offspring with a specific trait


Example: hybrid rice that produces greater yield and another hybrid rice
that contains greater nutritional properties


Disadvantage: Time
-
consuming and expensive


Inbreeding
: crossing closely related parent organisms who have been
bred to have desired traits to ensure that the traits are passed on


Example: German shepherd dogs


Disadvantage: Undesirable recessive traits are often passed down with
the desirable traits.


Selective Breeding


A process by which an organism’s DNA is manipulated in order
to insert the DNA of another organism (
creates recombinant
DNA
)


Purpose
: Incorporate the desirable traits of one organism into
another organism


Example
: Bioluminescent trait


A type of jellyfish contains a
protein (GFP: green fluorescent protein) that causes it to glow.
Scientists insert the DNA that codes for GFP into the DNA of
mosquito larvae so that they will glow. Mosquito populations can
be controlled as the larvae are more easily located.


Produces “genetically modified organisms”

Genetic Engineering


Selective breeding and genetic engineering require scientists
to use special tools or processes to manipulate DNA.


Restriction Enzymes
: cut DNA into smaller fragments with
“sticky ends” that allow it to connect to other fragments of DNA


Gel Electrophoresis
: electrical currents separate DNA fragments
based on size allowing fragments to be sorted and studied

DNA Tools

Useful in genetic engineering
where DNA of one organism is
inserted into the DNA of another
organism (
recombinant DNA
)

Example
:
EcoRI

restriction
enzyme cuts a GAATTC
sequence

Restriction
Enzymes

Restriction enzymes are found naturally
in bacteria cells. The bacteria developed
the enzymes to fight against viruses.
They chop up the viral DNA that gets
inserted into their cells.

Electrical currents run through
the DNA samples that have been
cut into fragments. Smaller
fragments travel more quickly
from the


electrode to the +
electrode.

Gel
Electrophoresis

Separated fragments can be studied or
combined with other fragments to create
recombinant DNA.


When a particular new DNA sequence has been developed in
recombinant DNA, bacteria cells are used to make multiple
copies.


The bacteria cells are heated which causes pores to open in their cell walls.


The recombinant DNA moves through the pores into the bacteria cell.


As the bacteria cell replicates, the recombinant DNA is replicated, too.


Purpose
: to create many copies of the desirable sequence
that can be used in genetically
-
modified organisms

Gene Cloning


Learning the sequence of DNA fragments can allow scientists
to understand the function of certain sequences of bases.


Restriction enzymes are used to cut large DNA strands into
shorter fragments.


Dyes are used to color known bases, and the known colored
known bases bind to the unknown sequence. The unknown
sequence can be read by following complementary base
-
pairing rules.


DNA Sequencing


Purpose
: create copies of selected DNA segments when the
sample size of DNA is too small to run all of the needed tests


Uses a thermal cycler to separate the DNA double helix and
DNA polymerase enzymes to create copies of the selected
segments.


Extremely useful in forensic science and medicine

Polymerase Chain Reaction


Purpose
: Insert beneficial genes into a needy organism


How?


A mutated gene is located on a chromosome.


A “normal” gene is inserted into a chromosome to replace the
dysfunctional one using a “viral vector.”


The virus infects a cell and injects its genetic material including the
“normal” gene. The cell begins replicated the “normal” gene, and
the mutation is corrected.

Gene Therapy